1. Field of the Invention
The present invention relates to recordable information storage media, and more particularly, to an information storage medium which minimizes an influence of optimal power control (OPC) process executed in an OPC area included in each of information storage layers upon other information storage layers of the information storage medium.
2. Description of the Related Art
General information storage media are widely used as information recording media of optical pickup apparatuses for recording/reproducing data in a non-contact way. Optical disks are used as the information storage medium and classified as compact disks (CDs) or digital versatile disks (DVDs) according to their information storage capacity. Examples of recordable, erasable, and reproducible optical disks are 650 MB CD-R, CD-RW, 4.7 GB DVD+RW, and the like. Furthermore, high density-DVDs (HD-DVDs) having a recording capacity of 25 GB or greater are under development.
As described above, information storage media have been developed to have a greater recording capacity. The recording capacity of an information storage medium can be increased in two representative ways of: 1) reducing the wavelength of a recording beam emitted from a light source; and 2) increasing the numerical aperture of an objective lens. In addition, there is a way of forming a plurality of information storage layers.
FIGS. 1A and 1B schematically illustrate a dual-layered information storage medium having first and second information storage layers L0 and L1. The first and second information storage layers L0 and L1 include first and second optimal power control (OPC) areas 111 and 121, respectively, for obtaining optimal writing power and first and second defect management area (DMAs) 115 and 125, respectively. The first and second OPC areas 111 and 121 face each other (i.e, are disposed at a common radius relative to an inner or outer boundary of the information storage medium).
Data is recorded in the first and second OPC areas 111 and 121 using various levels of writing power to find the optimum writing power. Hence, data may be recorded with a higher level of power than the optimum writing power. Table 1 shows variations in the jitter characteristics of each of the first and second information storage layers L0 and L1 when data is recorded in the OPC areas 111 and 121 with different levels of writing power.
TABLE 1Writing power about 20% higherNormal writing powerthan normal writing powerL0WritingUnwrittenWritingWrittenWritingWrittenL1UnwrittenWritingWrittenWritingWrittenWritingJitterL05.9%6.0%5.8%5.9% −> 6.4%L16.3%6.2%6.3%6.2% −> 6.3%WritingL06.46.36.37.56.4PowerL16.06.06.26.07.2
According to Table 1, if data is recorded with normal writing power, the jitter characteristics of the first or second information storage layer L0 or L1 keep constant. On the other hand, if data is recorded with writing power about 20% higher than the normal writing power, the jitter characteristics of the OPC area of the first or second information storage layer L0 or L1 in which data has already been recorded are degraded. If data is recorded on one of the first and second information storage layers L0 and L1 with writing power more than 20% higher than the normal writing power, it can be expected that the jitter characteristics of the other information storage layer may be further degraded.
Hence, if the first and second OPC areas 111 and 121 of the first and second information storage layers L0 and L1 exist within an equal radius as shown in FIGS. 1A and 1B, one of them may not be usable.
The recording status of one of the first and second OPC areas 111 and 121 may affect the recording characteristics of the other OPC area. For example, as shown in FIG. 1B, if data has been recorded on a part 111a of the first OPC area 111 and no data has been recorded on the residual area 111b thereof, the recording property of a part of the second OPC area 121 which corresponds to the occupied part 111a of the first OPC area 111 is different from that of a part of the second OPC area 121 which corresponds to the unoccupied part 111b of the first OPC area 111. In other words, since the transmittance of a laser with respect to the occupied part 111a of the first OPC area 111 is different from the transmittance of a laser with respect to the unoccupied part 111b thereof, the recording property of the second OPC area 121 may be irregular over the area.
As described above, if the first and second OPC areas are disposed within an equal radius, they may not properly function.